A carbon dioxide removal system maintains carbon dioxide (CO2) concentration at a safe level. Maintaining CO2 at safe levels can be accomplished by passing exhaled or inhaled gases through a canister filled with a chemical adsorbent, such as soda lime or anhydrous lithium hydroxide (LiOH). Several manufacturers make these adsorbents and use their own special mixes. For example, SODASORB®, manufactured by W. R. Grace & Co., is composed of a mixture of sodium hydroxide, calcium hydroxide, and potassium hydroxide.
Adsorbents are typically in the form of small granules that are generally sized between 0.04 to 0.25 inches (1.0 to 6.5 mm; 1 to 18 mesh) in diameter. The granules may be poured directly into a canister for scrubbing CO2. The gas to be scrubbed is forced through the granules either by lung power or by fan supplied power. Due to the generation of airborne caustic dust, the handling or pouring of granules in confined spaces is an undesirable operation.
Pre-filled granular cartridges offer the ease of use characteristics over loose granules, but these pre-filled canisters still have issues with shipping and handling or in-use shock and vibration, which causes chemical dusting of the adsorbent, settling of adsorbent which changes pressure drop, channeling of gases around the adsorbent (along the outer wall), all of which result in variable adsorbent performance. Pre-filled cartridges are installed into a canister/outer housing for use within equipment for scrubbing of CO2.
An alternative to granular adsorbent is the ExtendAir® adsorbent cartridge (Micropore Inc.). This technology as generally described in U.S. Pat. No. 5,964,221 solves all of the aforementioned issues which granular adsorbents have, while also providing the ease of use characteristics desired.
For many applications, an ExtendAir® adsorbent sheet is wound on a cylindrical core, but is sometimes stacked to form a cube or other shapes. The adsorbent is prevented from unwinding or losing shape by using an inexpensive polymer film wrapped around the exterior of the cartridge. This cartridge has ease of handling advantages offered by the pre-filled granular canisters and reduces or eliminates dusting, without the added manufacturing cost and bulk, of a completely enclosing plastic or metal housing.
However, the ends of the adsorbent cartridge assembly may become damaged during shipping, handling or even in-use. Further, the size or shape of the cartridge may not allow use of the cartridge with canisters of different shapes or sizes than that of the cartridge. In addition, for certain applications, the adsorbent material of the cartridge may be incompatible with direct contact with the canister material. Finally, it is desirable to produce an assembly that enables a uniform end seal or perimeter seal surface, without blocking perimeter flow channels. In the case of a cylindrical adsorbent cartridge, the seal would have to accommodate the step in the spirally wound cartridge, resulting from the outermost layer of the adsorbent sheet material.
Hence, there is a need for improved adsorbent cartridges to meet these needs. This invention addresses these needs and others.